Quantification of [99Tc]TcO4- in urine by means of anion-exchange chromatography-aerosol desolvation nebulization-inductively coupled plasma-mass spectrometry

To sensitively determine 99Tc, a new method for internal quantification of its most common and stable species, [99Tc]Tc O 4 - , was developed. Anion-exchange chromatography (IC) was coupled to inductively coupled plasma-mass spectrometry (ICP-MS) and equipped with an aerosol desolvation system to provide enhanced detection power. Due to a lack of commercial Tc standards, an isotope dilution-like approach using a Ru spike and called isobaric dilution analysis (IBDA) was used for internal quantification of 99Tc. This approach required knowledge of the sensitivities of 99Ru and 99Tc in ICP-MS. The latter was determined using an in-house prepared standard manufactured from decayed medical 99mTc-generator eluates. This standard was cleaned and preconcentrated using extraction chromatography with TEVA resin and quantified via total reflection X-ray fluorescence (TXRF) analysis. IC coupled to ICP-MS enabled to separate, detect and quantify [99Tc]Tc O 4 - as most stable Tc species in complex environments, which was demonstrated in a proof of concept. We quantified this species in untreated and undiluted raw urine collected from a patient, who previously underwent scintigraphy with a 99mTc-tracer, and determined a concentration of 19.6 ± 0.5 ng L-1. The developed method has a high utility to characterize a range of Tc-based radiopharmaceuticals, to determine concentrations, purity, and degradation products in complex samples without the need to assess activity parameters of 99(m)Tc.

A novel radiolabelled salmochelin derivative for bacteria-specific PET imaging: synthesis, radiolabelling and evaluation

For specific imaging of bacterial infections we aimed at targeting the exclusive bacterial iron transport system via siderophore-based radiotracers. De novo synthesis and radiolabeling yielded the salmochelin-based PET radiotracer [68Ga]Ga-RMA693, which showed a favourable biodistribution and a bacteria-specific uptake in an animal model of Escherichia coli infection.

Dual Emissive Zn(II) Naphthalocyanines: Synthesis, Structural and Photophysical Characterization with Theory-Supported Insights towards Soluble Coordination Compounds with Visible and Near-Infrared Emission

Metal phthalocyaninates and their higher homologues are recognized as deep-red luminophores emitting from their lowest excited singlet state. Herein, we report on the design, synthesis, and in-depth characterization of a new class of dual-emissive (visible and NIR) metal naphthalocyaninates. A 4-N,N-dimethylaminophen-4-yl-substituted naphthalocyaninato zinc(II) complex (Zn-NMe2Nc) and the derived water-soluble coordination compound (Zn-NMe3Nc) exhibit a near-infrared fluorescence from the lowest ligand-centered state, along with a unique push-pull-supported luminescence in the visible region of the electromagnetic spectrum. An unprecedentedly broad structural (2D-NMR spectroscopy and mass spectrometry) as well as photophysical characterization (steady-state state and time-resolved photoluminescence spectroscopy) is presented. The unique dual emission was assigned to two independent sets of singlet states related to the intrinsic Q-band of the macrocycle and to the push-pull substituents in the molecular periphery, respectively, as predicted by TD-DFT calculations. In general, the elusive chemical aspects of these macrocyclic compounds are addressed, involving both reaction conditions, thorough purification, and in-depth characterization. Besides the fundamental aspects that are investigated herein, the photoacoustic properties were exemplarily examined using phantom gels to assess their tomographic imaging capabilities. Finally, the robust luminescence in the visible range arising from the push-pull character of the peripheral moieties demonstrated a notable independence from aggregation and was exemplarily implemented for optical imaging (FLIM) through time-resolved multiphoton micro(spectro)scopy.

Infection Imaging: Focus on New Tracers?

Infections account for relevant morbidity and mortality, especially if the cardiovascular system is affected. Clinical manifestations are often unspecific, resulting in a challenging diagnostic work-up. The use of molecular imaging methods, namely [18F]FDG PET and leukocyte scintigraphy, is increasingly recognized in recently published international guidelines. However, these 2 established methods focus on the host's immune response to the pathogen and are therefore virtually unable to differentiate infection from inflammation. Targeting the microorganism responsible for the infection directly with novel imaging agents is a promising strategy to overcome these limitations. In this review, we discuss clinically approved [18F]FDG PET with its advantages and limitations in cardiovascular infections, followed by new PET-based approaches for the detection of cardiovascular infections by bacteria-specific molecular imaging methods. A multitude of different targeting options has already been preclinically evaluated, but most still lack clinical translation. We give an overview not only on promising tracer candidates for noninvasive molecular imaging of infections but also on issues hampering clinical translation.

Concerning the photophysics of fluorophores towards tailored bioimaging compounds: a case study involving S100A9 inflammation markers

A full understanding concerning the photophysical properties of a fluorescent label is crucial for a reliable and predictable performance in biolabelling applications. This holds true not only for the choice of a fluorophore in general, but also for the correct interpretation of data, considering the complexity of biological environments. In the frame of a case study involving inflammation imaging, we report the photophysical characterization of four fluorescent S100A9-targeting compounds in terms of UV-vis absorption and photoluminescence spectroscopy, fluorescence quantum yields (ΦF) and excited state lifetimes (τ) as well as the evaluation of the radiative and non-radiative rate constants (kr and knr, respectively). The probes were synthesized based on a 2-amino benzimidazole-based lead structure in combination with commercially available dyes, covering a broad color range from green (6-FAM) over orange (BODIPY-TMR) to red (BODIPY-TR) and near-infrared (Cy5.5) emission. The effect of conjugation with the targeting structure was addressed by comparison of the probes with their corresponding dye-azide precursors. Additionally, the 6-FAM and Cy5.5 probes were measured in the presence of murine S100A9 to determine whether protein binding influences their photophysical properties. An interesting rise in ΦF upon binding of 6-FAM-SST177 to murine S100A9 enabled the determination of its dissociation equilibrium constant, reaching up to KD = 324 nM. This result gives an outlook for potential applications of our compounds in S100A9 inflammation imaging and fluorescence assay developments. With respect to the other dyes, this study demonstrates how diverse microenvironmental factors can severely impair their performance while rendering them poor performers in biological media, showing that a preliminary photophysical screening is key to assess the suitability of a particular luminophore.

Do German university medical centres promote robust and transparent research? A cross-sectional study of institutional policies

Background

In light of replication and translational failures, biomedical research practices have recently come under scrutiny. Experts have pointed out that the current incentive structures at research institutions do not sufficiently incentivise researchers to invest in robustness and transparency and instead incentivise them to optimize their fitness in the struggle for publications and grants. This cross-sectional study aimed to describe whether and how relevant policies of university medical centres in Germany support the robust and transparent conduct of research and how prevalent traditional metrics are.

Methods

For 38 German university medical centres, we searched for institutional policies for academic degrees and academic appointments as well as websites for their core facilities and research in general between December 2020 and February 2021. We screened the documents for mentions of indicators of robust and transparent research (study registration; reporting of results; sharing of research data, code and protocols; open access; and measures to increase robustness) and for mentions of more traditional metrics of career progression (number of publications; number and value of awarded grants; impact factors; and authorship order).

Results

While open access was mentioned in 16% of PhD regulations, other indicators of robust and transparent research were mentioned in less than 10% of institutional policies for academic degrees and academic appointments. These indicators were more frequently mentioned on the core facility and general research websites. Institutional policies for academic degrees and academic appointments had frequent mentions of traditional metrics.

Conclusions

References to robust and transparent research practices are, with a few exceptions, generally uncommon in institutional policies at German university medical centres, while traditional criteria for academic promotion and tenure still prevail.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12961-022-00841-2.

Expanding Theranostic Radiopharmaceuticals for Tumor Diagnosis and Therapy

Radioligand theranostics (RT) in oncology use cancer-type specific biomarkers and molecular imaging (MI), including positron emission tomography (PET), single-photon emission computed tomography (SPECT) and planar scintigraphy, for patient diagnosis, therapy, and personalized management. While the definition of theranostics was initially restricted to a single compound allowing visualization and therapy simultaneously, the concept has been widened with the development of theranostic pairs and the combination of nuclear medicine with different types of cancer therapies. Here, we review the clinical applications of different theranostic radiopharmaceuticals in managing different tumor types (differentiated thyroid, neuroendocrine prostate, and breast cancer) that support the combination of innovative oncological therapies such as gene and cell-based therapies with RT.

Tumor-Cell-Specific Targeting of Ibrutinib: Introducing Electrostatic Antibody-Inhibitor Conjugates (AiCs)

Ibrutinib is an inhibitor of Bruton's tyrosine kinase that has been approved for the treatment of patients with chronic lymphocytic leukemia, mantle cell lymphoma and Waldenstrom's macroglobulinemia and is connected with toxicities. To minimize its toxicities, we linked ibrutinib to a cell‐targeted, internalizing antibody. To this end, we synthesized a poly‐anionic derivate, ibrutinib‐Cy3.5, that retains full functionality. This anionic inhibitor is complexed by our anti‐CD20‐protamine targeting conjugate and free protamine, and thereby spontaneously assembles into an electrostatically stabilized vesicular nanocarrier. The complexation led to an accumulation of the drug driven by the CD20 antigen internalization to the intended cells and an amplification of its pharmacological effectivity. In vivo, we observed a significant enrichment of the drug in xenograft lymphoma tumors in immune‐compromised mice and a significantly better response to lower doses compared to the original drug.

Sources of Information and Health Care Experiences Related to COVID-19 among Women Involved in Criminal Legal System in Three U.S. Cities

Women in the United States criminal legal (CL) system are at the nexus of several drivers of the COVID-19 pandemic, including incarceration, poverty, chronic illness and racism. There are 1.25 million women incarcerated or on community supervision (probation or parole) in the U.S. We present findings regarding the impact of COVID-19 on women in the CL system (N=344) during the early days of the pandemic. Participants were drawn from community settings in an ongoing study of cervical cancer risk in three U.S. cities: Birmingham, Alabama, Oakland, California and Kansas City, which straddles the states of Kansas and Missouri. Regional differences were found in COVID-19 testing and perceived susceptibility to the virus, but not in COVID-related disruptions to health care. We found differences by race/ethnicity in trusted sources of information about COVID. Black women had higher odds of choosing TV as their most trusted source of information, while White women were more likely to cite government or social service agencies as their most trusted source. Notably, 15% of women said they did not trust any source of information regarding COVID-19. COVID-19 disproportionately impacts populations with high levels of mistrust towards medical and government institutions, a result of the twin legacies of medical mistreatment and structural racism. Our findings underscore the need for innovative strategies to reach these groups with accurate and timely information.

Conjugated Pt(II) Complexes as Luminescence-Switch-On Reporters Addressing the Microenvironment of Bacterial Biofilms

In this work, the synthesis, structural and photophysical characterization of six phosphorescent H₂O-soluble Pt(II) complexes are reported while addressing their emission maxima, photoluminescence quantum yields (Φ_L), lifetimes (τ), aggregation tendency, and microenvironment sensitivity as a function of the substitution pattern on the main tridentate luminophore. Different ancillary ligands, namely, a trisulfonated phosphane and maltohexaose-conjugated pyridines (with or without amide bridges), were introduced and evaluated for the realization of switch-on-photoluminescent labels reporting on the microenvironment sensed in biofilms of Gram⁺ and Gram^- models, namely, Staphylococcus aureus and Escherichia coli. With the aid of confocal luminescence micro(spectro)scopy, we observed that selected complexes specifically interact with the biofilms while leaving planktonic cells unlabeled. By using photoluminescence lifetime imaging microscopy, excited-state lifetimes within S. aureus biofilms were measured. The photoluminescence intensities were drastically boosted, and the excited state lifetimes were significantly prolonged upon binding to the viscous biofilm matrix, mainly due to the suppression of radiationless deactivation pathways upon shielding from physical quenching processes, such as interactions with solvent molecules and ³O₂. The best performances were attained for non-aggregating complexes with maltohexaose targeting units and without amide bridges. Notably, in the absence of the maltodextrin, a hydrophobic adamantyl moiety suffices to attain a sizeable labeling capacity. Moreover, photoluminescence studies showed that selected complexes can also effectively interact with E. coli biofilms, where the bacterial cells are able to partially uptake the maltodextrin-based agents. In summary, the herein introduced concepts enable the development of specific biofilm reporters providing spatial resolution as well as lifetime- and spectrum-based readouts. Considering that most theragnostic agents reported so far mainly address metabolically active bacteria at the surface of biofilms but without reaching cells deeply immersed in the matrix, a new platform with a clear structure-property correlation is provided for the early detection of such bacterial arrays.

Naphthalonitriles featuring efficient emission in solution and in the solid state

In this work, a series of γ-substituted diphenylnaphthalonitriles were synthesized and characterized. They show efficient emission in solution and in the aggregated state and their environment responsiveness is based on having variable substituents at the para-position of the two phenyl moieties. The excited state properties were fully investigated in tetrahydrofuran (THF) solutions and in THF/H₂O mixtures. The size of the aggregates in aqueous media were measured by dynamic light scattering (DLS). The steady-state and time-resolved photoluminescence spectroscopy studies revealed that all the molecules show intense fluorescence both in solution and in the aggregated state. In THF solutions, a blue emission was observed for the unsubstituted (H), methyl- (Me) and tert-butyl- (t-Bu) substituted γ-diphenylnaphthalonitriles, which can be attributed to a weak π-donor capability of these groups. On the other hand, the methoxy- (OMe), methylsulfanyl- (SMe) and dimethylamino- (NMe₂) substituted compounds exhibit a progressive red-shift in emission compared to H, Me and t-Bu due to a growing π-electron donating capability. Interestingly, upon aggregation in water-containing media, H, Me and t-Bu show a slight red-shift of the emission and a blue-shift is observed for OMe, SMe and NMe₂. The crystal structure of Me allowed a detailed discussion of the structure–property relationship. Clearly, N-containing substituents such as NMe₂ possess more electron-donating ability than the S-based moieties such as SMe. Moreover, it was found that NMe₂ showed higher luminescence quantum yields (Φ_F) in comparison to SMe, indicating that N-substituted groups could enhance the fluorescence intensity. Therefore, the π-donor nature of the substituents on the phenyl ring constitutes the main parameter that influences the photophysical properties, such as excited state lifetimes and photoluminescence quantum yields. Hence, a series of highly luminescent materials from deep blue to red emission depending on substitution and environment is reported with potential applications in sensing, bioimaging and optoelectronics.

Enhancing glycan stability via site-selective fluorination: modulating substrate orientation by molecular design

Single site OH → F substitution at the termini of maltotetraose leads to significantly improved hydrolytic stability towards α-amylase and α-glucosidase relative to the natural compound. To explore the effect of molecular editing, selectively modified oligosaccharides were prepared via a convergent α-selective strategy. Incubation experiments in purified α-amylase and α-glucosidase, and in human and murine blood serum, provide insight into the influence of fluorine on the hydrolytic stability of these clinically important scaffolds. Enhancements of ca. 1 order of magnitude result from these subtle single point mutations. Modification at the monosaccharide furthest from the probable enzymatic cleavage termini leads to the greatest improvement in stability. In the case of α-amylase, docking studies revealed that retentive C2-fluorination at the reducing end inverts the orientation in which the substrate is bound. A co-crystal structure of human α-amylase revealed maltose units bound at the active-site. In view of the evolving popularity of C(sp³)–F bioisosteres in medicinal chemistry, and the importance of maltodextrins in bacterial imaging, this discovery begins to reconcile the information-rich nature of carbohydrates with their intrinsic hydrolytic vulnerabilities.

Single site OH → F substitution at the termini of maltotetraose leads to significantly improved hydrolytic stability towards α-amylase and α-glucosidase relative to the natural compound.

Initial experience with [18F]DPA-714 TSPO-PET to image inflammation in primary angiitis of the central nervous system

Purpose

Primary angiitis of the central nervous system (PACNS) is a heterogeneous, rare, and poorly understood inflammatory disease. We aimed at non-invasive imaging of activated microglia/macrophages in patients with PACNS by PET-MRI targeting the translocator protein (TSPO) with [¹⁸F]DPA-714 to potentially assist differential diagnosis, therapy monitoring, and biopsy planning.

Methods

In total, nine patients with ischemic stroke and diagnosed or suspected PACNS underwent [¹⁸F]DPA-714-PET-MRI. Dynamic PET scanning was performed for 60 min after injection of 233 ± 19 MBq [¹⁸F]DPA-714, and MRI was simultaneously acquired.

Results

In two PACNS patients, [¹⁸F]DPA-714 uptake patterns exceeded MRI correlates of infarction, whereas uptake was confined to the infarct in four patients where initial suspicion of PACNS could not be confirmed. About three patients with PACNS or cerebral predominant lymphocytic vasculitis showed no or only faintly increased uptake. Short-term [¹⁸F]DPA-714-PET follow-up in a patient with PACNS showed reduced lesional [¹⁸F]DPA-714 uptake after anti-inflammatory treatment. Biopsy in the same patient pinpointed the source of tracer uptake to TSPO-expressing immune cells.

Conclusions

[¹⁸F]DPA-714-PET imaging may facilitate the diagnosis and treatment monitoring of PACNS. Further studies are needed to fully understand the potential of TSPO-PET in deciphering the heterogeneity of the disease.

Electronic supplementary material

The online version of this article (10.1007/s00259-019-04662-4) contains supplementary material, which is available to authorized users.

Oxygen-Insensitive Aggregates of Pt(II) Complexes as Phosphorescent Labels of Proteins with Luminescence Lifetime-Based Readouts

The synthesis and photophysical properties of a tailored Pt(II) complex are presented. The phosphorescence of its monomeric species in homogeneous solutions is quenched by interaction with the solvent and therefore absent even upon deoxygenation. However, aggregation-induced shielding from the environment and suppression of rotovibrational degrees of freedom trigger a phosphorescence turn-on that is not suppressed by molecular oxygen, despite possessing an excited-state lifetime ranging in the microsecond scale. Thus, the photoinduced production of reactive oxygen species is avoided by the suppression of diffusion-controlled Dexter-type energy transfer to triplet molecular oxygen. These aggregates emit with the characteristic green luminescence profile of monomeric complexes, indicating that Pt-Pt or excimeric interactions are negligible. Herein, we show that these aggregates can be used to label a model biomolecule (bovine serum albumin) with a microsecond-range luminescence. The protein stabilizes the aggregates, acting as a carrier in aqueous environments. Despite spectral overlaps, the green phosphorescence can be separated by time-gated detection from the dominant autofluorescence of the protein arising from a covalently bound green fluorophore that emits in the nanosecond range. Interestingly, the aggregates also acted as energy donors able to sensitize the emission of a fraction of the fluorophores bound to the protein. This resulted in a microsecond-range luminescence of the fluorescent acceptors and a shortening of the excited-state lifetime of the phosphorescent aggregates. The process that can be traced by a 1000-fold increase in the acceptor's lifetime mirrors the donor's triplet character. The implications for phosphorescence lifetime imaging are discussed.

Axially Decorated SiIV -phthalocyanines Bearing Mannose- or Ammonium-conjugated Siloxanes: Comparative Bacterial Labeling and Photodynamic Inactivation<sup/>

Herein, we present a comparative study about the photoinactivation of Staphylococcus aureus (Gram-positive model) and Escherichia coli (Gram-negative model) employing a neutral and a dicationic axially functionalized Si^IV -phthalocyanine. Depending on the charge of the siloxane moiety (neutral monosaccharide or cationic ammonium salt), different interactions with the bacteria were observed, and a differential photoinactivation was facilitated. The intensity of the fluorescence labeling correlated with the photoinactivation of the two types of bacteria: While the neutral species only significantly affected the Gram-positive cells, we observed that the positively charged photosensitizer interacted both with the Gram-positive and with the Gram-negative models. The dicationic photosensitizer labeled both models with a characteristic deep-red fluorescence and photoinactivated both classes of prokaryotes. In general, our study clearly demonstrates that axially ammoniumsiloxane-functionalized Si(IV) phthalocyaninates constitute excellent photosensitizers due to their weak aggregation in aqueous environments. In particular, we also show that charge-based targeting with axial ammonium groups leads toward broad-spectrum Si^IV -phthalocyanines for photodynamic inactivation of bacteria.

Towards optimized naphthalocyanines as sonochromes for photoacoustic imaging in vivo

In this paper we establish a methodology to predict photoacoustic imaging capabilities from the structure of absorber molecules (sonochromes). The comparative in vitro and in vivo screening of naphthalocyanines and cyanine dyes has shown a substitution pattern dependent shift in photoacoustic excitation wavelength, with distal substitution producing the preferred maximum around 800 nm. Central ion change showed variable production of photoacoustic signals, as well as singlet oxygen photoproduction and fluorescence with the optimum for photoacoustic imaging being nickel(II). Our approach paves the way for the design, evaluation and realization of optimized sonochromes as photoacoustic contrast agents.

Optical imaging probes and their potential contribution to radiotracer development

Optical imaging has long been considered a method for histological or microscopic investigations. Over the last 15 years, however, this method was applied for preclinical molecular imaging and, just recently, was also able to show its principal potential for clinical applications (e.g. fluorescence-guided surgery). Reviewing the development and preclinical evaluation of new fluorescent dyes and target-specific dye conjugates, these often show characteristic patterns of their routes of excretion and biodistribution, which could also be interesting for the development and optimization of radiopharmaceuticals. Especially ionic charges show a great influence on biodistribution and netcharge and charge-distribution on a conjugate often determines unspecific binding or background signals in liver, kidney or intestine, and other organs.

Learning from fluorescent probe behaviour in vivo and translating this knowledge to radio-pharmaceuticals might be useful to further optimize emerging and existing radiopharmaceuticals with respect to their biodistribution and thereby availability for binding to their targets.

Isobaric dilution analysis as a calibration tool for long lived radionuclides in ICP-MS

A novel quantification method named isobaric dilution analysis (IBDA) is introduced for internal calibration using inductively coupled plasma mass spectrometry (ICP-MS). Unlike isotope dilution analysis (IDA), where a sample to be analysed for a target analyte element is spiked with an isotopically enriched solution of the same element, IBDA uses the fact that conventional mass analysers cannot distinguish between two isobaric isotopes of different elements. Therefore, in IBDA, the sample with the element of interest is spiked with a solution of a different element, which shares at least one isobaric isotope and shows similar chemical properties resulting in a similar response. This method offers a less expensive alternative to conventional IDA especially for long-lived radionuclides of elements for which a spiking element that fulfils the above mentioned requirements can be provided. In addition, IBDA offers the advantage of making certain metastable, sometimes monoisotopic elements accessible to internal calibration using a strategy analogous to IDA. One of the elements accessible by the new calibration strategy is technetium (Tc), which suffers from a lack of standards due to safety requirements associated with its radioactivity. In this work, the principle of IBDA is first demonstrated for a certified gadolinium standard, which was diluted with a dysprosium spike exhibiting an isobaric isotope with m/z 160. The results obtained by IBDA were compared with those obtained by a conventional IDA. The concept of IBDA was subsequently used for the determination of ⁹⁹Tc in a contrast agent. Since no certified Tc standards are available, the response of ⁹⁹Tc was interpolated allowing accurate determinations with an uncertainty of 1%.

Combined PET Imaging of the Inflammatory Tumor Microenvironment Identifies Margins of Unique Radiotracer Uptake

The tumor microenvironment is highly heterogeneous. For gliomas, the tumor-associated inflammatory response is pivotal to support growth and invasion. Factors of glioma growth, inflammation, and invasion, such as the translocator protein (TSPO) and matrix metalloproteinases (MMP), may serve as specific imaging biomarkers of the glioma microenvironment. In this study, noninvasive imaging by PET with [¹⁸F]DPA-714 (TSPO) and [¹⁸F]BR-351 (MMP) was used for the assessment of localization and quantification of the expression of TSPO and MMP. Imaging was performed in addition to established clinical imaging biomarker of active tumor volume ([¹⁸F]FET) in conjunction with MRI. We hypothesized that each imaging biomarker revealed distinct areas of the heterogeneous glioma tissue in a mouse model of human glioma. Tracers were found to be increased 1.4- to 1.7-fold, with [¹⁸F]FET showing the biggest volume as depicted by a thresholding-based, volumes of interest analysis. Tumor areas, which could not be detected by a single tracer and/or MRI parameter alone, were measured. Specific compartments of [¹⁸F]DPA-714 (14%) and [¹⁸F]BR-351 (11%) volumes along the tumor rim could be identified. [¹⁸F]DPA-714 (TSPO) and [¹⁸F]BR-351 (MMP) matched with histology. Glioma-associated microglia/macrophages (GAM) were identified as TSPO and MMP sources. Multitracer and multimodal molecular imaging approaches may allow us to gain important insights into glioma-associated inflammation (GAM, MMP). Moreover, this noninvasive technique enables characterization of the glioma microenvironment with respect to the disease-driving cellular compartments at the various disease stages. Cancer Res; 77(8); 1831-41. ©2017 AACR.

New molecular probes of vascular inflammation

New molecular imaging approaches featuring the assessment of inflammatory processes in the vascular wall on top of existing anatomic and functional vessel imaging procedures could emerge as decisive tools for the understanding and prevention of cardiovascular events. In this respect imaging approaches addressing specific molecular and cellular targets in atherosclerosis are of high interest. This review summarizes the rationale and current status of nuclear imaging probes which possess high translational potential.

6-hydroxydopamine-induced Parkinson's disease-like degeneration generates acute microgliosis and astrogliosis in the nigrostriatal system but no bioluminescence imaging-detectable alteration in adult neurogenesis

Parkinson's disease is a slowly progressing neurodegenerative disorder caused by loss of dopaminergic neurons in the substantia nigra (SN), leading to severe impairment in motor and non-motor functions. Endogenous subventricular zone (SVZ) neural stem cells constantly give birth to new cells that might serve as a possible source for regeneration in the adult brain. However, neurodegeneration is accompanied by neuroinflammation and dopamine depletion, potentially compromising regeneration. We therefore employed in vivo imaging methods to study striatal deafferentation (N-ω-fluoropropyl-2β-carbomethoxy-3β-(4-[(123) I]iodophenyl)nortropane single photon emission computed tomography, DaTscan(™) ) and neuroinflammation in the SN and striatum (N,N-diethyl-2-(2-(4-(2-[(18) F]fluoroethoxy)phenyl)-5,7-dimethylpyrazolo[1,5-a]pyrimidin-3-yl)acetamide positron emission tomography, [(18) F]DPA-714 PET) in the intranigral 6-hydroxydopamine Parkinson's disease mouse model. Additionally, we transduced cells in the SVZ with a lentivirus encoding firefly luciferase and followed migration of progenitor cells in the SVZ-olfactory bulb axis via bioluminescence imaging under disease and control conditions. We found that activation of microglia in the SN is an acute process accompanying the degeneration of dopaminergic cell bodies in the SN. Dopaminergic deafferentation of the striatum does not influence the generation of doublecortin-positive neuroblasts in the SVZ, but generates chronic astrogliosis in the nigrostriatal system.

Labeling and Selective Inactivation of Gram-Positive Bacteria Employing Bimodal Photoprobes with Dual Readouts

Carbohydrate-conjugated silicon(IV) phthalocyanines with bimodal photoactivity were developed as probes with both fluorescent labeling and photosensitizing capabilities, and the concomitant fluorescent labeling and photoinduced inactivation of Gram-positive and Gram-negative models was explored. The maltohexaose-conjugated photoprobe provides a dual readout to distinguish between both groups of pathogens, as only the Gram-positive species was inactivated, even though both appeared labeled with near-infrared luminescence. Antibiotic resistance did not hinder the phototoxic effect, as even the methicillin-resistant pathogen Staphylococcus aureus (MRSA) was completely photoinactivated. Time-resolved confocal fluorescence microscopy analysis suggests that the photoprobe sticks onto the outer rim of the microorganisms, explaining the resistance of Gram-negative species on the basis of their membrane constitution. The mannose-conjugated photoprobe yields a different readout because it is able to label and to inactivate only the Gram-positive strain.

A combined experimental and computational study of the substituent effect on the photodynamic efficacy of amphiphilic Zn(ii)phthalocyanines

The interplay between structural features, photophysical characteristics and photodynamic efficacy of carbohydrate substituted amphiphilic Zn(ii)phthalocyanines is presented.

Optical imaging probes and their potential contribution to radiotracer development

Optical imaging has long been considered a method for histological or microscopic investigations. Over the last 15 years, however, this method was applied for preclinical molecular imaging and, just recently, was also able to show its principal potential for clinical applications (e .g. fluorescence-guided surgery). Reviewing the development and preclinical evaluation of new fluorescent dyes and target-specific dye conjugates, these often show characteristic patterns of their routes of excretion and biodistribution, which could also be interesting for the development and optimization of radiopharmaceuticals. Especially ionic charges show a great influence on biodistribution and net-charge and charge-distribution on a conjugate often determines unspecific binding or background signals in liver, kidney or intestine, and other organs. Learning from fluorescent probe behaviour in vivo and translating this knowledge to radiopharmaceuticals might be useful to further optimize emerging and existing radiopharmaceuticals with respect to their biodistribution and thereby availability for binding to their targets.

Synthesis, binding affinity and structure-activity relationships of novel, selective and dual targeting CCR2 and CCR5 receptor antagonists

CCR2 and CCR5 receptors play a key role in the development and progression of several inflammatory, cardiovascular and autoimmune diseases. Therefore, dual targeting of both receptors appeals as a promising strategy for the treatment of such complex, multifactorial disorders. Herein we report on the design, synthesis and biological evaluation of benzo[7]annulene- and [7]annulenothiophene-based selective and dual CCR2 and CCR5 receptor antagonists. Intermediates were designed in such a way that diversification could be introduced at the end of the synthesis. Starting from the lead compound TAK-779 (1), the quaternary ammonium moiety was exchanged by different non-charged moieties, the 4-methylphenyl moiety was extensively modified and the benzo[7]annulene core was replaced bioisosterically by the [7]annulenothiophene system. The naphthyl derivative 9h represents the most promising dual antagonist (Ki (CCR2) = 25 nM, IC50 (CCR5) = 17 nM), whereas the 6-isopropoxy-3-pyridyl and 4-methoxycarbonylphenyl derivatives 9k and 9r show more than 20-fold selectivity for the CCR2 (Ki = 19 nM) over the CCR5 receptor.

Multimodal imaging reveals temporal and spatial microglia and matrix metalloproteinase activity after experimental stroke

Stroke is the most common cause of death and disability from neurologic disease in humans. Activation of microglia and matrix metalloproteinases (MMPs) is involved in positively and negatively affecting stroke outcome. Novel, noninvasive, multimodal imaging methods visualizing microglial and MMP alterations were employed. The spatio-temporal dynamics of these parameters were studied in relation to blood flow changes. Micro positron emission tomography (μPET) using [(18)F]BR-351 showed MMP activity within the first days after transient middle cerebral artery occlusion (tMCAo), followed by increased [(18)F]DPA-714 uptake as a marker for microglia activation with a maximum at 14 days after tMCAo. The inflammatory response was spatially located in the infarct core and in adjacent (penumbral) tissue. For the first time, multimodal imaging based on PET, single photon emission computed tomography, and magnetic resonance imaging revealed insight into the spatio-temporal distribution of critical parameters of poststroke inflammation. This allows further evaluation of novel treatment paradigms targeting the postischemic inflammation.

Development and evaluation of a non-peptidic ligand for the molecular imaging of inflammatory processes using S100A9 (MRP14) as a novel target

We describe the development and first evaluation of a novel S100A9 specific molecular imaging probe (Cy5.5-CES271) for optical imaging of local inflammatory activity in vivo.

Molecular imaging reveals time course of matrix metalloproteinase activity in acute cutaneous vasculitis in vivo

Matrix metalloproteinases (MMPs) play a critical role in various pathological conditions including cutaneous inflammation. Thus far, serial assessment of MMP activity in ongoing inflammation is hampered due to technical limitations. Here, we present an innovative method for longitudinal detection of MMP activity by in vivo imaging. First, we analysed skin sections from patients suffering from leucocytoclastic vasculitis (LcV) and detected a significant MMP signal via immunofluorescence staining. Then, we mimicked LcV in mice in a well-studied model of immune complex-mediated vasculitis (ICV). This acute inflammatory process was serially visualized in vivo using the fluorescence-labelled MMP tracer Cy5.5-AF443. The deposition of fluorescence-labelled immune complexes and MMP tracer distribution was visualized repeatedly and non-invasively by fluorescence reflectance imaging. In correlation with the presence of MMP-2 and MMP-9 in immunofluorescence stainings, Cy5.5-AF443 accumulated in ICV spots in the skin of C57BL/6 mice. This tracer accumulation could also be observed in mice equipped with a dorsal skinfold chamber, where microscopic observations revealed an increased recruitment of fluorescence-labelled leucocytes during ICV. The specificity of the MMP tracer was supported by (i) analysis of mice deficient in functional β2 -integrins (CD18(-/-) ) and (ii) subsequent MMP immunofluorescence staining. These findings let us conclude that MMP accumulation in the acute phase of ICV depends on β2 -mediated leucocyte recruitment. In summary, we show that MMPs are involved in ICV as determined by Cy5.5-AF443, a new optical marker to longitudinally and non-invasively follow MMP activity in acute skin inflammation in vivo.

Alarmin S100A8/S100A9 as a biomarker for molecular imaging of local inflammatory activity

Inflammation has a key role in the pathogenesis of various human diseases. The early detection, localization and monitoring of inflammation are crucial for tailoring individual therapies. However, reliable biomarkers to detect local inflammatory activities and to predict disease outcome are still missing. Alarmins, which are locally released during cellular stress, are early amplifiers of inflammation. Here, using optical molecular imaging, we demonstrate that the alarmin S100A8/S100A9 serves as a sensitive local and systemic marker for the detection of even sub-clinical disease activity in inflammatory and immunological processes like irritative and allergic contact dermatitis. In a model of collagen-induced arthritis, we use S100A8/S100A9 imaging to predict the development of disease activity. Furthermore, S100A8/S100A9 can act as a very early and sensitive biomarker in experimental leishmaniasis for phagocyte activation linked to an effective Th1-response. In conclusion, the alarmin S100A8/S100A9 is a valuable and sensitive molecular target for novel imaging approaches to monitor clinically relevant inflammatory disorders on a molecular level.

Specific biomarkers of receptors, pathways of inhibition and targeted therapies: pre-clinical developments

A deeper understanding of the role of specific genes, proteins, pathways and networks in health and disease, coupled with the development of technologies to assay these molecules and pathways in patients, promises to revolutionise the practice of clinical medicine. Especially the discovery and development of novel drugs targeted to disease-specific alterations could benefit significantly from non-invasive imaging techniques assessing the dynamics of specific disease-related parameters. Here we review the application of imaging biomarkers in the management of patients with brain tumours, especially malignant glioma. In our other review we focused on imaging biomarkers of general biochemical and physiological processes related with tumour growth such as energy, protein, DNA and membrane metabolism, vascular function, hypoxia and cell death. In this part of the review, we will discuss the use of imaging biomarkers of specific disease-related molecular genetic alterations such as apoptosis, angiogenesis, cell membrane receptors and signalling pathways and their application in targeted therapies.

Efficient synthesis of a fluorine-18 labeled biotin derivative

INTRODUCTION

The natural occurring vitamin biotin, also known as vitamin H or vitamin B(7), plays a major role in various metabolic reactions. Caused by its high binding affinity to the protein avidin with a dissociation constant of about 10(-15)M the biotin-avidin system was extensively examined for multiple applications. We have synthesized a fluorine-18 labeled biotin derivative [(18)F]4 for a potential application in positron emission tomography (PET).

METHODS

Mesylate precursor 3 was obtained by an efficient two-step reaction via a copper catalyzed azide-alkyne cycloaddition (CuAAC) from easily accessible starting materials. [(18)F]4 was successfully synthesized by a nucleophilic radiofluorination of precursor 3. A biodistribution study by means of small-animal PET imaging in wt-mice was performed and serum stability was examined.

RESULTS

Compound [(18)F]4 was obtained from precursor compound 3 with an average specific activity of 16GBq/μmol within 45min and a radiochemical yield of 45±5% (decay corrected). [(18)F]4 demonstrated only negligible decomposition in human serum. A qualitative binding study revealed the high affinity of the synthesized biotin derivative to avidin. Blocking experiments with native biotin showed that binding was site-specific. Biodistribution studies showed that [(18)F]4 was cleared quickly and efficiently from the body by hepatobiliary and renal elimination.

CONCLUSION

An efficient synthesis for [(18)F]4 was established. In vivo characteristics were determined and demonstrated the pharmacokinetic behaviour of [(18)F]4.

Synthesis and evaluation of a novel hydroxamate based fluorescent photoprobe for imaging of matrix metalloproteinases

The assessment of matrix metalloproteinase (MMP) activity in vivo is highly desirable in various human diseases such as cancers. Hydroxamic acids based on CGS27023A or CGS25966 are nonpeptidyl lead structures that specifically target activated MMPs in vivo. The aim of this study was the modification and fluorescent labeling of these lead structures to develop a highly affine, nonpeptide MMP inhibitor (MMPI)-ligand for molecular optical imaging of activated MMPs. An 11 step synthesis was developed involving a PEGylated benzyl derivative as a spacer to minimize the interactions between the activated MMP and the dye of conjugate 11 with an azide as a protected amino function. After reducing the azide (Staudinger reaction) and labeling with Cy5.5, we obtained a CGS-based MMP inhibitor 11 with a fluorescent signaling flag. To evaluate the biological properties of this photoprobe, three human cancer cell lines (A-673, HT-1080 and BT-20) were characterized with respect to their MMP-2 and -9 (gelatinases) expression levels (real-time PCR) and protein levels (Western blotting). Initially, fluorogenic inhibition assays were used to assess the MMP inhibition potential. The PEGylated CGS 10 showed complete inhibition of MMP-2 and MMP-9 activities in vitro both for purified MMP-2/-9 (active and pro-forms) and MMP-2/-9 containing cell culture supernatants. To test the imaging potential in biological tissues, gelatinase activity was measured on tumor cryostat sections of the above-mentioned tumor cells using FITC-labeled dye-quenched gelatin. Gelatinase positive tumors revealed strong binding of CGS-Cy5.5 11, while gelatinase negative tumors were not targeted. In conclusion, this new CGS-based MMP photoprobe has a high affinity for MMP-2 and -9 and is thus a promising candidate for sensitive imaging of MMP activity in various diseases in patients.